Network elements are commonly used in a telecommunication network to transfer communication signals between various locations (such as cities or suburbs within a city). One or more such network elements may be located physically within a central office of a local telephone company, and are coupled to other central offices via trunks and/or backbone. Each central office is normally connected to telephone instruments of subscribers in nearby locations. For distant neighborhoods (of homes or businesses), the local telephone company installs electronic components outside the central office, at locations called “drop sites.” Such electronic components (which may be part of a device called “digital loop carrier” abbreviated as DLC) are typically supported on line cards that in turn are mounted in shelves (also called “card cages”) housed within outdoor enclosures (also called “cabinets”).
Outdoor enclosures that house DLCs may be mounted on a pole, or mounted on a pad of concrete in the ground. Such outdoor enclosures (also called “cabinets”) are normally manufactured of heavy guage mill-galvanized steel with moisture and inset barrier base, overhanging rain guards, closed cell neoprene door gasketing, and screened louvers. For example, Marconi Communications, Inc. has a series of cabinets called MESA. Alcatel also has a line of such enclosures, called LITESPAN, described at, for example, www.usa.alcatel.com. See also, for example, U.S. Pat. No. 5,781,410 granted to Keown et al. and U.S. Pat. No. 4,901,202 granted to Leschinger each of which describes telecommunication cabinets, and each of which is incorporated by reference herein in its entirety.
Local telephone companies now have tens of thousands of such outdoor enclosures in suburban and rural areas. First generation DLCs, such as Lucent's SLC® systems were introduced in the late 1970s. Newer fiber-fed DLCs (also called NGDLCs) were introduced the late 1980s to shorten the copper loops to individual residences. The copper loops supported by DLCs or NGDLCs can be used to provide various services in addition to plain old telephone service (POTS), such as digital subscriber line (DSL). Specifically, voice and data are transmitted simultaneously on a single telephone line, and the central office separates the two types of traffic: low frequency voice traffic is sent to a voice switch while high frequency data traffic is sent to a DSL access multiplexer (abbreviated as DSLAM).
However, cabinets that currently house such DLCs and NGDLCs often lack sufficient space for DSL equipment. Right-of-way issues, aesthetics and high costs (e.g. in pouring new concrete pads or installing additional poles, and obtaining additional electrical power) discourage local telephone companies from installing additional cabinets to support DSL services. In response, telephone equipment vendors have begun to integrate DSLAM functionality into DLC line cards. Integrated line cards may be specifically engineered as card-for-card replacements, such that there is no reduction in POTS (plain old telephone service) capacity. See for example, an integrated line card called “CNX-5” available from Catena Networks. See also U.S. Pat. No. 6,295,343 granted to Hjartarson, et al. that is incorporated by reference herein in its entirety.
Moreover, U.S. Pat. No. 5,729,370 granted to Bernstein and Coy on Mar. 17, 1998 describes a “Method For Upgrading A Communication Network”, and is incorporated by reference herein in its entirety. See also U.S. Pat. No. 5,911,019 granted to Cohen, and U.S. Pat. No. 6,314,102 granted to Czerwiec et al each of which is also incorporated by reference herein in its entirety.